TypeScript Modules

TypeScript follows the ES Modules (ESM) specification for modularizing code, while maintaining support for legacy formats like CommonJS.

Defining a Module

Any file containing a top-level import or export is considered a module. Files without them are treated as scripts with shared global scope.

ES Module Syntax

• export default: The main export of a file.
• export: Named exports for variables, functions, and types.
• import: Consume exports from other files.
• import * as name: Import all exports into a single namespace.
• export { ... } from './file': Re-exporting items.

TypeScript Specifics

• import type: Ensures a reference is only used as a type and can be safely removed by non-TS transpilers.
• Inline type imports: import { someValue, type someType } from './file'.

CommonJS Syntax

The format used by Node.js and many npm packages.

• module.exports = { ... }: Exporting items.
• const math = require('./math'): Importing items.
• import fs = require('fs'): TypeScript's syntax for CommonJS interoperability.

Module Resolution

The process of mapping an import string to a file on disk. Strategies include Node (replicating Node.js logic) and Classic.

Namespaces

A TypeScript-specific way to organize code that pre-dates ESM. Primarily used today in definition files (.d.ts) on DefinitelyTyped.

References

• Source: 00_Raw/typescript-handbook.md
• typescript-moc
• typescript-compiler-options